There are an ever-growing number of new applications that use high bandwidth digital and analog electro-optic systems. For example, in digital computing systems, electro-optic systems are often utilized to route signals among processors. In analog systems, electro-optic systems are often utilized in applications, such as phased array radar. Electro-optic systems are also commonly found in applications that switch high bandwidth optical carriers in communication systems.
In these systems, light beams are modulated in a digital and/or analog fashion and are used as “optical carriers” of information. An important component in these systems is the optical source or transmitter. Conventional semiconductor lasers have found widespread use in these systems as the light source of choice. For example, semiconductor lasers are commonly found in communications systems, compact disc players, and many other devices and systems.
Several types of surface emitting lasers have been developed. One commonly known and utilized is referred to as a “vertical cavity surface emitting laser” (VCSEL). VCSELs have many advantages over other types of optical sources. First, VCSELs can be fabricated in arrays with relative ease as compared to edge emitting devices that are not as easily fabricated. For example, an array of VCSELs can be fabricated by growing the desired layers on a substrate and then patterning the layers to form the array. Individual lasers may be separately connected with appropriate contacts. These arrays are useful in diverse applications as, for example, image processing inter-chip communications and optical interconnects.
For certain applications, it is desirable to use large one-dimensional or two-dimensional transmitter arrays. VCSELs can be easily made into one-dimensional and two-dimensional arrays. In fact, nice two-dimensional VCSEL arrays have been demonstrated. Furthermore, localized yields for VCSELs have increased into the high 90% range, thereby making the creation of two-dimensional arrays more practical.
Unfortunately, for very large two-dimensional array, the manufacturing yield issues remain challenging. Specifically, as the number of individual lasers in an array is increased, the probability that at least one of the lasers will not operate correctly due to manufacturing defects also increases. When one assumes that device failures are the result of wafer defects, then one would expect individual VCSELs to have yields as high as 99.6%. However, the expected yield for a 10×10 array is about 67%, while the expected yield for a 20×20 array drops to about 20%. Consequently, achieving acceptable manufacturing yields in large laser arrays is extremely difficult.
It is desirable for there to be a mechanism that increases the manufacturing yield for a VCSEL arrays, especially large VCSEL arrays.
Based on the foregoing, there remains a need for a transmitter array with at least one pixel element that has a primary semiconductor laser and at least one secondary semiconductor laser and that overcomes the disadvantages set forth previously.